My experience with my A550, which is loaded with SD and MS duo cards, is that with my camera during shooting, there is no discernable difference between the two at all - that's in JPEG or RAW, and using continuous frame mode. The buffer will eventually fill at 15 or so RAW files and slow the camera down a bit - neither card seems to make any difference in that rate. In JPEG, it'll shoot 7fps for far longer than I ever need it to, so I've never hit a limit. I notice no speed issues compared to my A300 with CF cards.

I can't say I notice any real difference loading from the SD or MS card to my computer either - though possibly there are several seconds difference when loading 1,000 shots. Honestly, I don't really care about that!

I bought enough card to support what my camera needed - enough to not hinder the camera's performance specs, while not more than necessary just to avoid spending extra money for no real benefit. As it happens, the A550 works just fine with Ultra II SD and Mark II Pro Duo MS.

All the super 60x extreme premium firewire etc may be faster in certain cameras or for downloading/uploading...but I didn't really care about any of that - I wanted to be able to get 100% performance out of my camera with no memory card slowing it down, and those two cards both do the work.

And contrary to the other oft-quoted problem with memory stick...the Sony branded MS card was cheaper than the Sandisk SD card for the same capacity and speed! It's a common mantra leveed against memory stick for years, that they were so much more expensive...but at least now, the playing field appears leveled.